Manufacture Method of NDFEB Isotropic and Anisotropic Permanent Magnets

ABSTRACT

A fabrication method of isotropic and anisotropic NdFeB type permanent magnets is disclosed. In the a fabrication method of isotropic and anisotropic NdFeB type permanent magnets, the isotropic and anisotropic NdFeB type permanent magnets can be easily manufactured by means of Joule&#39;s heat using a self resistance of a powder molded body by directly applying a DC (Direct Current) to the upper and lower punches and the powder molded body, without using external heating elements or high frequency coils and so on, during press molding of the permanent magnet powder using the punches, and it is simple in terms of structure during the fabrication thereof, so that the manufacturing cost is low.

TECHNICAL FIELD

The present invention relates to a fabrication method of isotropic and anisotropic NdFeB type permanent magnets, and more particularly to a fabrication method of isotropic and anisotropic NdFeB type permanent magnets in which the isotropic permanent magnets is manufactured in such a manner that a powder molded body of a freeform type, in which a NdFeB type powder based on Nd₂Fe₁₄B ferromagnetic phase is compression molded in normal temperature, is putted into a graphite mold, predetermined pressure and electric current are applied to the powder molded body through upper and lower punches, and the powder molded body is contracted in the pressure direction, and the anisotropic permanent magnet is manufactured in such a manner that an isotropic permanent magnet molded body is adhered and fixed between upper and lower punches, the isotropic permanent magnet molded body is heated by applying a DC to the upper and lower punches, a predetermined pressure is applied to the upper and lower punches, and the molded body is contracted in the pressure direction of the upper and lower punches and expanded perpendicularly to the pressure direction of the upper and lower punches, whereby the isotropic and anisotropic NdFeB type permanent magnets can be easily manufactured by means of Joule's heat using a self resistance of a powder molded body by directly applying a DC (Direct Current) to the upper and lower punches and the powder molded body, without using external heating elements or high frequency coils and so on, during press molding of the permanent magnet powder using the punches, and it is simple in terms of structure, during the fabrication thereof, so that the manufacturing cost is low.

BACKGROUND ART

Generally, a manufacturing process of a permanent magnet includes a hot process for manufacturing an isotropic magnet (see FIG. 1) and a hot deformation process for manufacturing an anisotropic magnet, in which the isotropic magnet manufactured by the hot process is compressed and transformed in high temperature and pressure as shown in FIG. 2.

However, since the hot process and hot deformation process are performed in a high temperature of about 700° C. and a high pressure over 1 ton/cm², it is necessary to raise the temperature by winding heater coils 40 into a vessel containing a powder 10, or to make a desired temperature circumstance and apply a high pressure by placing high frequency coils 40 at the periphery of a mold, so that it is extremely restricted to use a graphite mold having a small strength. Also, because it is impossible to use a molding aid of a special material, the material of the mold must use a metal or ceramic. Moreover, in a case of damaging the mold, an alternative cost is very high. Furthermore, in order to make manufactured goods of a desired shape, there is a defect in that the treatment process is essentially required, after the completion of manufacture goods.

In the meantime, in order to improve the above problems, a fabrication method of a permanent magnet by means of Joule's heat using a powder and a self resistance of a mold proposed by the present inventors had been registered as a patent in that a DC (Direct Current) is directly applied to a permanent magnet powder or a permanent magnet molded body through an electrical device, without using external heating elements or high frequency coils, during press molding of the permanent magnet powder.

That is, as shown in FIG. 3, Korean Patent No. 10-0424142 has been disclosed in that rare earth magnets are putted into the mold, a pressure of 50-150 Mpa is applied to the upper and lower punches 2 and 3, and a DC of 450-4,000 A/cm² is applied to the mold through the upper and lower punches 2 and 3 by means of the electrical device 4, thereby obtaining a permanent magnet 5 of a bulk status from the powder.

However, where predetermined pressure and electric current are applied to the powder 1 putted into the mold through the upper and lower punches 2 and 3 at the same time, since the pressure is applied to the mold and the powder before the permanent magnet powder expanded perpendicularly to the pressure direction is plastic deformed, there is defects in that it is difficulty to manufacture the permanent magnet and a permanent magnet 5 of a bulk status having high purity and density.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a fabrication method of isotropic and anisotropic NdFeB type permanent magnets, in which the isotropic and anisotropic NdFeB type permanent magnets can be easily manufactured by means of Joule's heat using a self resistance of a powder molded body by directly applying a DC (Direct Current) to the powder molded body, without using external heating elements or high frequency coils and so on, during the fabrication thereof, and it is simple in terms of structure, during the fabrication thereof, thereby the manufacturing cost is low.

Technical Solution

To accomplish the object, the present invention provides a fabrication method of an isotropic NdFeB type permanent magnet, comprising the steps of: putting a powder molded body of a freeform type, in which a NdFeB type powder is compression molded in normal temperature, into a graphite mold; adhering and fixing the powder molded body to upper and lower punches located at upper and lower parts thereof; applying a DC of 500-3,000 A/cm² to the upper and lower punches, whereby generating a resistance heat of 700-800° C. into the powder molded body; applying a pressure of 10-150 Mpa to the upper and lower punches; and cooling the isotropic permanent magnet, in which the powder molded body is contracted in the pressure direction of the upper and lower punches.

Here, the isotropic permanent magnet, in which the powder molded body is contracted in the pressure direction of the upper and lower punches, is cooled in normal temperature.

Also, the material of the mold for fixing the powder molded body is a metal or ceramic.

To accomplish the object, the present invention provides a fabrication method of an anisotropic NdFeB type permanent magnet, comprising the steps of: adhering and fixing a molded body of an isotropic permanent magnet between upper and lower punches; applying a DC of 500-3,000 A/cm² to the upper and lower punches, whereby generating a resistance heat of 700-800° C. into the molded body; and applying a pressure of 50-200 Mpa to the upper and lower punches, whereby contracting the molded body in the pressure direction of the upper and lower punches and expanding the molded body perpendicularly to the pressure direction of the upper and lower punches.

Advantageous Effects

As can be seen from the foregoing, in the fabrication method of isotropic and anisotropic NdFeB type permanent magnet, there are superior effects in that the isotropic and anisotropic NdFeB type permanent magnets can be easily manufactured by means of Joule's heat using a self resistance of a powder molded body by directly applying a DC (Direct Current) to the powder molded body, without using external heating elements or high frequency coils and so on, during the fabrication thereof, and it is simple in terms of structure, during the fabrication thereof, thereby the manufacturing cost is low.

While this invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above as well as the other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view illustrating a fabrication method of a permanent magnet according to a conventional hot press process;

FIG. 2 is a schematic perspective view illustrating a fabrication method of a permanent magnet according to a conventional hot deformation process;

FIG. 3 is a schematic perspective view illustrating a fabrication method of a permanent magnet according to a conventional current applying;

FIG. 4 is a schematic perspective view illustrating a fabrication method of an isotropic NdFeB type permanent magnet according to the present invention; and

FIG. 5 is a schematic perspective view illustrating a fabrication method of an anisotropic NdFeB type permanent magnet according to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the invention will be described in detail below with reference to the accompanying drawings.

FIG. 4 is a schematic perspective view illustrating a fabrication method of an isotropic NdFeB type permanent magnet according to the present invention. A NdFeB type permanent magnet powder, which is manufactured by rapidly solidifying the NdFeB type permanent magnet based on Nd₂Fe₁₄B ferromagnetic phase, or a powder molded body 110 of a freeform type, in which the NdFeB type permanent magnet powder is compression molded in normal temperature, are putted into a graphite mold 120. In this case, the powder molded body 110, which is putted into the graphite mold 120, is adhered and fixed to upper and lower punches 130 and 140 located at upper and lower parts thereof.

Here, instead of the graphite mold 110, a ceramic mold of metal or nonmetal may be used.

As described above, the powder molded body 110 adhered and fixed to the upper and lower punches 130 and 140 is plastic-worked in such a manner that a DC (Direct Current) of 500-3,000 A/cm² is applied to the upper and lower punches 130 and 140 through an electrical device 150, so as to generate a resistance heat of 700-800° C. into the powder molded body 110. Simultaneously with this, a pressure of 10-150 Mpa is pressurized to the upper and lower punches 130 and 140 to mold the isotropic NdFeB type permanent magnet 160, in which the powder molded body 110 is contracted in the pressure direction of the upper and lower punches 130 and 140.

Here, the reason for heating the resistance heat at 700-800° C. is because that the plastic deformation of the powder molded body 110 cannot be generated into the graphite mold 120 or can be degraded.

Also, it is preferred that the DC applied to the upper and lower punches 130 and 140 through the electrical device 150 is 500-3,000 A/cm². However, the present invention is not limited to any intensity of the DC, it can be properly changed according to the diameter size per unit area of the powder molded body 110 and so on, which is located inside the graphite mold 120.

As described above, where the contraction of the isotropic NdFeB type permanent magnet 160 is completed, the supply of the DC is blocked and the contracted permanent magnet 160 is cooled at a normal temperature, so that the molded boy of the isotropic permanent magnet 160 is obtained.

FIG. 5 is a schematic perspective view illustrating a fabrication method of an anisotropic NdFeB type permanent magnet according to another embodiment of the present invention.

As shown in FIG. 5, a molded body 210 of an isotropic type permanent magnet is adhere and fixed between upper and lower punches 230 and 240 and then, the molded body 210 of an isotropic type permanent magnet adhered and fixed between the upper and lower punches 230 and 240 is plastic-worked in such a manner that a DC (Direct Current) of 500-3,000 A/cm² is applied to the upper and lower punches 230 and 240 through an electrical device 250.

As described above, the DC applied to the upper and lower punches 230 and 240 is flowed into the molded body 210 of an isotropic type permanent magnet and a resistance heat of 700-800° C. is generated into the molded body 210 of the isotropic NdFeB type permanent. Thereafter, where the temperature of the molded body 210 of the isotropic NdFeB type permanent magnet reaches a predetermined firing temperature, a pressure of 50-200 Mpa is pressurized to the upper and lower punches 230 and 240 to mold the anisotropic NdFeB type permanent magnet 220, in which the molded body 210 is contracted in the pressure direction of the upper and lower punches 230 and 240 and is expanded perpendicularly to the pressure direction of the upper and lower punches 230 and 240.

Here, the reason for heating the resistance heat at 700-800° C. is because that the plastic deformation of the molded body 210 cannot be generated into the graphite mold 120 or can be degraded.

Also, it is preferred that the DC applied to the upper and lower punches 130 and 140 through the electrical device 150 is 500-3,000 A/cm². However, the present invention is not limited to any intensity of the DC, it can be properly changed according to the diameter size per unit area of the molded body 210.

As described above, where the contraction of the anisotropic NdFeB type permanent magnet 210 is completed, the supply of the DC is blocked so that the molded body of the isotropic permanent magnet 220 is obtained. 

1. A fabrication method of an isotropic NdFeB type permanent magnet, comprising the steps of: putting a powder molded body of a freeform type, in which a NdFeB type powder is compression molded in normal temperature, into a graphite mold; adhering and fixing the powder molded body to upper and lower punches located at upper and lower parts thereof; applying a DC of 500-3,000 A/cm² to the upper and lower punches, whereby generating a resistance heat of 700-800° C. into the powder molded body; applying a pressure of 10-150 Mpa to the upper and lower punches; and cooling the isotropic permanent magnet, in which the powder molded body is contracted in the pressure direction of the upper and lower punches.
 2. The method as claimed in claim 1, wherein the isotropic permanent magnet, in which the powder molded body is contracted in the pressure direction of the upper and lower punches, is cooled in normal temperature.
 3. The method as claimed in claim 1, wherein a material of the mold for fixing the powder molded body is a metal or ceramic.
 4. A fabrication method of an anisotropic NdFeB type permanent magnet, comprising the steps of: adhering and fixing a molded body of an isotropic permanent magnet between upper and lower punches; applying a DC of 500-3,000 A/cm² to the upper and lower punches, whereby generating a resistance heat of 700-800° C. into the molded body; and applying a pressure of 50-200 Mpa to the upper and lower punches, whereby contracting the molded body in the pressure direction of the upper and lower punches and expanding the molded body perpendicularly to the pressure direction of the upper and lower punches. 